“We stopped teaching people to do crunches a long, long time ago,” says Dr. Richard Guyer, president of the Texas Back Institute. Why? It's simple: the actual “crunch” part of crunches puts an unwanted strain on your back at its weakest point - the spot on your spine with the most nerves, and highest potential for damage.

 

Hupert is dismayed when the girls aren't fooled.

 

“There are only so many bends or a ‘fatigue life’,” in your spinal disks,” says Stuart M. McGill, a professor of spine biomechanics at the University of Waterloo and author of  the book Ultimate Back Fitness and Performance. Inside each disk is a mucus-like nucleus, he says, and “if you keep flexing your spine and bending the disk over and over again, that nucleus slowly breaches the layers and causes a disk bulge, or a disk herniation.”  A herniated disk won’t be visible, but it's likely to cause persistent back and leg pain, weakness, and tingling.

 

“When people are doing curl-ups over gym balls and sit-ups, they are replicating a very potent injury mechanism on their back,” says McGill. “Every time they bend it they are one repetition closer to damaging the disk.”

 

Not only can it be damaging to your spine, but crunches might not be the best solution for a flat stomach, either. That’s because doing too many sit-ups at the expense of other, more comprehensive movements can lead to the dreaded “aerobic abs.”  That’s the term celebrity trainer Steve Maresca coined to describe the distended stomachs of those who focus only on the rectus abdominus muscles targeted by sit-ups and crunches. “They look great from the front, but when they turn to the side, their stomachs are extended,” he says. 

 

Crunches do help build up a mass of muscle that's essential in protecting your internal organs, but chances are you won't be climbing into a cage-fighting match anytime soon. To have a really strong lower back, obliques and upper back, look into deadlifts. Like the pushup, the best exercises for back health and a firmer stomach are ones that work your abs while holding your spine straight.

 

Then again, strength really won't matter that much if your body fat is too high. Watch what you eat, make sure you incorporate a lot of cardio into your workout routine and steer clear of those crunches!